ATHENS, Oct 2 (Reuters) - Three senior lawmakers from Greece's far-right Golden Dawn were freed on Wednesday pending trial on criminal charges, an unexpected setback to the government's efforts to clamp down on a party it has labelled a neo-Nazi criminal gang.

The decision to free the men after an 18-hour court session raises questions about the solidity of the state's case against Golden Dawn after one of its sympathisers stabbed to death an anti-fascism rapper.

Party spokesman Ilias Kasidiaris and fellow lawmakers Ilias Panagiotaros and Nikos Michos stormed out of the court to cheers of "bravo" from supporters. They kicked and shoved journalists out of the way before hailing a taxi.

"We will not back down!" Michos shouted. "You can only stop us with bullets. Even from the grave, we will rise up - know this well!"

The unfolding saga has riveted a country where a crackdown on elected politicians has not been seen since a military coup nearly five decades ago.

Golden Dawn rose from being a fringe party to win 18 seats in parliament in last year's election. It has drawn on anger over the debt crisis, budget cuts, high unemployment and corruption to become what opinion polls indicate is Greece's third most popular party, but has lost about a third of its support since the killing.

The images of the men walking freely were in stark contrast to footage of the party's leaders handcuffed and hustled to police headquarters at the weekend.

"The political world is shocked," said Asimina Ksirotiri, a lawmaker from the Democratic Left party said in parliament.

In a letter by Golden Dawn leader Nikolaos Mihaloliakos written from his police cell and published on the party's website on Wednesday, he said the authorities would not succeed in their effort to undermine his party.

"The truth will ultimately shine, their plans will not pass. However this dark story ends, it is certain that we Golden Dawners made history and no one can take this away from us," he said.

Mihaloliakos later arrived at court flanked by hooded anti-terrorism policemen with machineguns.

"CRUSHING EXTREMISM"

Hundreds of flag-waving supporters were outside the court chanting the party's "Blood! Honour! Golden Dawn!" slogan as scores of police in riot gear stood guard. "Even in death, we will stand by you, leader!" a man shouted.

Kasidiaris was released on bail of 50,000 euros ($67,600). He, Michos and Ilias Panagiotaros were ordered not to leave Greece. A fourth Golden Dawn legislator, Yannis Lagos, was ordered to be kept in detention. All four denied the charges.

The four lawmakers were arrested on Saturday alongside Mihaloliakos and two dozen party members.

They have been charged on what prosecutors say is evidence linking the party with a series of attacks, including the stabbing of rapper Pavlos Fissas on Sept. 17 and the killing of an immigrant earlier this year. A trial date has not been set.

Prime Minister Antonis Samaras's government has vowed to wipe out a party of "Nazi descendents". It has shied away from trying to ban the party outright but has ordered investigations into it and plans to introduce laws against hate speech and deprive the party of state funding.

Samaras has said the government was "crushing extremism" and called Golden Dawn a "fascist, neo-fascist, neo-Nazi party whose leader is currently in jail."

Responding to the charges against him behind closed doors, Kasidiaris said he was a victim of political persecution and denied before the magistrate that the party had paramilitary-like "storm troops" trained by him, a court official said.

The party has been linked by human rights' groups to attacks on dark-skinned immigrants by gangs of Golden Dawn supporters dressed in black and wielding baseball bats.

Nazi memorabilia, including flags, helmets with swastikas and portraits of Adolph Hitler, have been found in the homes of arrested members, police said. The party rejects the neo-Nazi label.